1. Field of the Invention
The present invention relates to a wastewater treatment apparatus and method using a biological filtering process, and more particularly, to a batch style wastewater treatment apparatus and method using a biological filtering process.
2. Description of the Related Art
As a biological wastewater treatment process, there are suspended growth methods, in which suspended microorganisms are utilized. According to this technique, wastewater and microorganisms are mixed in a reaction tank and air is supplied from the bottom of the reaction tank, thereby facilitating contact between wastewater and microorganisms. The microorganisms present in the reaction tank are capable of removing pollutants using oxygen contained in the air supplied. A sequencing batch reactor (SBR) technique is one of the suspended growth methods.
FIG. 1 is a schematic representation of a sequencing batch reactor (SBR), for illustrating a wastewater treatment method using a SBR technique.
Referring to FIG. 1, wastewater to be treated is filled in a reaction tank 1 up to an inflow level Hi and the wastewater is aerated using an aerator 3 while stirring, to permit a reaction to occur. If the reaction is completed, sludge is precipitated, and supernatant liquid is decanted until the level of the reaction tank becomes an outflow level Ho, and then discharged. Then, before new wastewater is introduced into the reaction tank, the operation of the sequencing batch reactor is idled for a predetermined time in order to adjust a cycling time.
The SBR technique is a modified sequencing activated sludge process, in which an unsteady environmental pressure is applied to microbe consortia in a reaction tank for microbial selection, for overcoming problems arising from a heavy impact load, which may be generated during a sequencing activated sludge process, sedimentation from a settling reservoir and an increase in the settlement site area due to a secondary settling reservoir.
The SBR technique has advantages in terms of excellent impact absorbing ability and excellent sludge sedimentation capability. However, the SBR technique has the following problems.
First, the SBR technique involves complicated steps, including, wastewater filling; reaction, settlement, discharging and idling, requiring a long cycling time.
Second, a decanter for discharging treated water is required, which is economically inefficient and poor in stability.
Third, flow control is difficult due to a long cycling time.
Fourth, an objectionable smell is generated and floating scum is generated, making liquid-solid separation difficult.
Fifth, sludge may be easily drained during discharge or decanting.
Another biological wastewater treatment process includes a sequencing biological filtering method.
FIG. 2 shows a conventional wastewater treatment apparatus using a sequencing biological filtering process.
Referring to FIG. 2, a denitrification reaction in wastewater will be described. First, wastewater to be treated is introduced into a lower chamber 7 through a wastewater supply means 2 of a denitrification tank 5 in an anoxic condition and is allowed to upwardly pass through a filter medium layer 9. Here, nitrate nitrogen returned from a nitrification tank 11 through an internal returning means 23 is denitrified using organic matter in the wastewater and denitrifying microorganisms inhabiting in the filter medium layer 9.
Then, the wastewater having passed through the denitrification tank 5 is introduced into a lower chamber 13 of the nitrification tank 11 through a first discharging means 10. In this case, air is supplied to the nitrification tank 11 through a process air introducing means 17. The wastewater introduced into the lower chamber 13 is allowed to upwardly pass though the filter medium layer 15 and organic nitrogen and ammonium nitrogen contained therein are nitrified by nitrifying microorganisms.
Finally, the treated wastewater having passed through the nitrification tank 11 is discharged to a separate storage tank 21 through a second discharging means 19. The completely treated water is discharged from the storage tank 21. During backwashing, the treated water is introduced to the lower chamber 7 of the denitrification tank 5 and the lower chamber 13 of the nitrification tank 11 through a backwash water introducing means 25 to wash the filter medium layers 9 and 15. Then, the wastewater used in backwashing is discharged to the sedimentation tank or settling reservoir by a backwash water discharging means 27.
According to the sequencing biological filtering method implemented in the above-described manner, the wastewater can be effectively treated in terms of cost and performance since both physical filtering by a filter medium layer and biodegradation by microorganisms inhabiting in the filter medium layer are used for wastewater treatment, unlike in a sequencing physical filtering method in which only physical filtering by a filter medium is used.
Yet the sequencing biological filtering method has several problems.
First, biological removal of phosphorus due to phosphorus release and excessive uptake mechanism of a microbe membrane is impossible.
Second, nitrogen and phosphorus cannot be simultaneously removed in a single reaction tank.
Third, for the foregoing reason, at least two reaction tanks are required for wastewater treatment.
Fourth, clogging may be liable to occur to a filter medium layer, making it difficult to be suitably applied to high-concentration wastewater.
To solve the above-described problems, it is an object of the present invention to provide a batch style wastewater treatment apparatus using a biological filtering process.
It is another object of the present invention to provide a wastewater treatment method using the wastewater treatment apparatus.
To accomplish the first object, there is provided a wastewater treatment apparatus according to a first embodiment of the present invention.
The wastewater treatment apparatus includes a bottom portion and a plate formed above and spaced apart from the bottom portion to form a lower chamber with the bottom portion, an outlet installed on the bottom portion for drawing off water and sludge in the lower chamber before backwashing, a filter medium layer supported to the upper portion of the plate by the plate, the upper layer of which forms a bottom portion of an upper chamber, a wastewater introducing means connected to the lower chamber, for introducing wastewater to be treated into the lower chamber, a process air introducing means for supplying process air to the filter medium layer formed over the plate, a plurality of aerators formed over and spaced apart a predetermined distance from the plate, and mounted in a plurality of air flow pipes led to the process air introducing means, a backwash air introducing means for supplying backwash air to the lower chamber during backwashing, a backwash water introducing means for supplying backwash water to the lower chamber during backwashing, a plurality of nozzles extending from the lower chamber to the filter medium layer through the plate, a treated water discharging means for discharging the treated water having passed through the filter medium layer, and a returned water introducing means for returning the treated water having passed through the filter medium layer to the lower chamber.
To accomplish the above object, the present invention also provides a modification of the wastewater treatment apparatus according to the first embodiment of the present invention. That is to say, a wastewater treatment apparatus according to a second embodiment of the present invention includes a bottom portion and a plate formed above and spaced apart from the bottom portion to form a lower chamber with the bottom portion, an outlet installed on the bottom portion for drawing off water and sludge in the lower chamber before backwashing, a filter medium layer supported to the upper portion of the plate by the plate, the upper layer of which forms a bottom portion of an upper chamber, a process air introducing means for supplying process air to the filter medium layer formed over the plate, a plurality of aerators formed over and spaced apart a predetermined distance from the plate, and mounted in a plurality of air flow pipes led to the process air introducing means, a backwash air introducing means for supplying backwash air to the lower chamber during backwashing, a backwash water introducing means for supplying backwash water to the lower chamber during backwashing, a plurality of nozzles extending from the lower chamber to the filter medium layer through the plate, a treated water discharging means for discharging the treated water having passed through the filter medium layer, a returned water introducing means for returning the treated water having passed through the filter medium layer to the lower chamber, and a wastewater introducing means connected to the returned water introducing means, for introducing wastewater to be treated into the lower chamber.
In the wastewater treatment apparatuses according to the first and second embodiment of the present invention, the filter medium layer is preferably upwardly passed through by the wastewater to be treated, treated water or mixed water thereof, with or without process air, during normal operation, and the filter medium layer is preferably upwardly passed through by backwash air and backwash water during backwashing.
Also, the plurality of aerators may uniformly distribute process air in the form of fine bubbles for creating optimum conditions for growth of microorganisms during normal operation, and may include means for preventing a counterflow of the treated water during backwashing even if supply of the process air or backwash air is inhibited.
The plurality of nozzles preferably supply the wastewater to be treated, treated water or mixed water thereof, from the lower chamber to the filter medium layer, during normal operation, and preferably include means for forming an air layer having a predetermined height at the lower chamber so as to uniformly distribute backwash air having a pressure high enough to dilate the filter medium layer, during backwashing.
The filter medium layer is preferably supported by a support layer having a predetermined height covering the aerators from the upper surface of the plate.
Also, the wastewater treatment apparatus may further include an water level adjusting means for automatically adjusting the water level of the upper chamber.
The side walls of the upper chamber preferably taper downward to maximize the capacity of treated water contained in the upper chamber.
The wastewater treatment apparatus may further include a storage tank for temporarily storing the treated water introduced through the returned water introducing means and then supplying the same to the lower chamber.
According to another aspect of the present invention, there is provided a wastewater treatment method including the steps of (a) introducing wastewater to be treated to the lower chamber through the wastewater introducing means of the wastewater treatment apparatus according to first or third embodiment of the present invention and allowing the wastewater to upwardly pass through the filter medium layer until the water level of the upper chamber reaches an inflow level, under anoxic conditions, (b) returning the wastewater contained in the upper chamber to the lower chamber through the returned water introducing means for circulation so as to allow upstream passage of the filter medium layer under anoxic/anaerobic conditions, to denitrify nitrate nitrogen remaining in the previous cycle using organic matter in the wastewater and denitrifying microorganisms in the filter medium layer and also to cause a phosphorus release reaction to occur using organic matter in the wastewater and subordinate phosphorus removing microorganisms in the filter medium layer, (c) returning the wastewater from the upper chamber to the lower chamber through the returned water introducing means and causing the returned wastewater to circulate for upstream passage of the filter medium layer, while supplying air through the process air introducing means, to nitrify organic nitrogen and ammonium nitrogen using nitrifying microorganisms and to cause an excessive uptake of phosphorus using subordinate phosphorus removing microorganisms, and (d) discharging the treated water through the treated water discharging means.
The wastewater treatment apparatuses according to the first and second embodiments of the present invention may further a storage tank for temporarily storing the wastewater introduced through the returned wastewater introducing means and then supplies the same to the lower chamber, these apparatuses according to third and fourth embodiments of the present invention, respectively.
Also, the present invention provides a wastewater treatment method including the steps of (a) introducing wastewater to be treated to the lower chamber through the wastewater introducing means connected to the returned water introducing means of the wastewater treatment apparatus according to the second or fourth embodiment of the present invention and allowing the wastewater to upwardly pass through the filter medium layer until the water level of an upper chamber reaches an inflow level, under non-aeration conditions, (b) returning the wastewater contained in the upper chamber to the lower chamber through a returned water introducing means for circulation so as to allow upstream passage of the filter medium layer under anoxic/anaerobic conditions, to denitrify nitrate nitrogen remaining in the previous cycle using organic matter in the wastewater and denitrifying microorganisms in the filter medium layer and also to cause a phosphorus release reaction to occur using organic matter in the wastewater and subordinate phosphorus removing microorganisms in the filter medium layer, (c) returning the wastewater from the upper chamber to the lower chamber through the returned water introducing means and causing the, returned wastewater to circulate for upstream passage of the filter medium layer, while supplying air through the process air introducing means, to nitrify organic nitrogen and ammonium nitrogen using nitrifying microorganisms and to cause an excessive uptake of phosphorus using subordinate phosphorus removing microorganisms, and (d) discharging the treated water from which organic matter, nitrogen and phosphorus are removed through a treated water discharging means.
In an another embodiment of the present invention, there is provided a wastewater treatment method including the steps of (a) while supplying air through the process air introducing means of the wastewater treatment apparatus according to the second or fourth embodiment of the present invention, introducing wastewater to be treated to the lower chamber through the wastewater introducing means and allowing the wastewater to upwardly pass through a filter medium layer until the water level of an upper chamber reaches an inflow level, (b) returning the wastewater from the upper chamber to the lower chamber through the returned water introducing means and causing the returned wastewater to circulate for upstream passage of the filter medium layer, while supplying air through the process air introducing means, to nitrify organic nitrogen and ammonium nitrogen using nitrifying microorganisms, and (c) discharging the treated water subjected to the nitrification through a treated water discharging means.
Alternatively, the present invention provides a wastewater treatment method including the steps of (a) while supplying air, introducing wastewater to be treated to a lower chamber through a wastewater introducing means connected to a returned water introducing means of the wastewater treatment apparatus according to the second or fourth embodiment of the present invention and allowing the wastewater to upwardly pass through a filter medium layer until the water level of an upper chamber reaches an inflow level, (b) returning the wastewater from the upper chamber to the lower chamber through the returned water introducing means and causing the returned wastewater to circulate for upstream passage of the filter medium layer, while supplying air through the process air introducing means, to nitrify organic nitrogen and ammonium nitrogen using nitrifying microorganisms, and (c) discharging the treated water subjected to the nitrification through a treated water discharging means.
According to another aspect of the present invention, there is provided a wastewater treatment method including the steps of (a) introducing wastewater to be treated to a lower chamber through a wastewater introducing means of the wastewater treatment apparatus according to the second or fourth embodiment of the present invention and allowing the wastewater to upwardly pass through a filter medium layer until the water level of an upper chamber reaches an inflow level, under non-aeration conditions, (b) returning the wastewater contained in the upper chamber to the lower chamber through a returned water introducing means for circulation so as to allow upstream passage of the filter medium layer under anoxic conditions, to denitrify nitrate nitrogen remaining in the previous cycle using organic matter in the wastewater and denitrifying microorganisms in the filter medium layer, (c) returning the wastewater from the upper chamber to the lower chamber through the returned water introducing means and causing the returned wastewater to circulate for upstream passage of the filter medium layer, while supplying air through the process air introducing means, to nitrify organic nitrogen and ammonium nitrogen using nitrifying microorganisms, and (d) discharging the treated water subjected to the nitrification through a treated water discharging means.
Alternatively, there is provided a wastewater treatment method including the steps of (a) under non-aeration conditions, introducing wastewater to be treated to a lower chamber through a wastewater introducing means connected to a returned water introducing means of the wastewater treatment apparatus according to the second or fourth embodiment of the present invention and allowing the wastewater to upwardly pass through a filter medium layer until the water level of an upper chamber reaches an inflow level, (b) returning the wastewater contained in the upper chamber to the lower chamber through a returned water introducing means for circulation so as to allow upstream passage of the filter medium layer under anoxic conditions, to denitrify nitrate nitrogen remaining in the previous cycle using organic matter in the wastewater and denitrifying microorganisms in the filter medium layer, (c) returning the wastewater from the upper chamber to the lower chamber through the returned water introducing means and causing the returned wastewater to circulate for upstream passage of the filter medium layer, while supplying air through the process air introducing means, to nitrify organic nitrogen and ammonium nitrogen using nitrifying microorganisms, and (d) discharging the treated water subjected to the nitrification through a treated water discharging means.
In the wastewater treatment method according to present invention, before supplying the wastewater to the wastewater treatment apparatus, there may be further included the step of introducing the wastewater to be treated to a settling tank for removal of some of suspended solid in the wastewater.
Also, after the discharging step, there may be further included the steps of supplying backwash air from the lower chamber to the filter medium layer through a backwash air introducing means and the plurality of nozzles to dilate the filter medium layer, stopping the supply of backwash air and supplying backwash water through the backwash water introducing means and the plurality of nozzles to backwash the filter medium layer.
The backwash water is preferably the treated water discharged by one of the wastewater treatment apparatuses according to the first through fourth embodiments of the present invention.
In the wastewater treatment method according to the present invention, the respective steps are preferably repeated by automatic operation by a programmable logic controller.